1. Field of the Invention
The present invention relates to an armature damper used for a wire dot printer, a method of manufacturing the armature damper and a dot head using the armature damper.
2. Description of the Related Art
The wire dot printer is arranged to move a printing wire (hereinafter, simply referred to as a wire) called a needle forward and backward to strike the tip end of the wire against a print medium thereby to print a dot-shaped image thereon. Since the wire dot printer employs such the printing method, the wire dot printer can simultaneously print plural slips etc. in a stacked state and so is employed for business use. Although there are various kinds of methods as the printing method of moving the wire (needle) forward and backward, the method called a clapper type is generally employed. The clapper type has been employed widely since the structure thereof is simple and a relatively long stroke can be secured. Such the kind of the printing method is proposed by JP-A-2005-75000, for example.
The dot head of such the clapper type includes armatures each for driving a corresponding wire backward and forward. The armature is pivotally supported at a portion near the one end thereof so as to be rotatable. The armature is provided with an attracted portion opposing to a core, at the intermediate portion between the pivotally supported portion and the free end of the armature. An arm is extended from the free end of the armature so as to be integrated with the armature. A needle for printing is provided at the tip end of the arm. The needle is attached to the arm in a manner that the axial direction of the needle crosses with the longitudinal direction of the arm at the tip end of the arm. The armature and the arm integrally provided with the armature rotate in the operation direction around the pivotally supported portion when the attracted portion is attracted by the magnetic force generated by the core. When the armature and the arm integrally provided with the armature rotate in the operation direction in this manner, the needle provided at the tip end of the arm moves forward. In contrast, when the magnetic force having been generated by the core disappears, the armature and the arm integrally provided with the armature rotate in the restoring direction by a spring force etc. and so the needle moves backward.
The dot head is arranged in a manner that a plurality of the armatures each thus configured are disposed radially around a print portion.
The dot head is provided with an armature damper in corresponding to the armatures. At the time of the rotation of the armature in the restoring direction, that is, at the time of the rotation of the needle in the backward moving direction, the armature damper abuts against the one side of the arm thereby to stop the arm at a predetermined backward position while absorbing the rebounding operation of the arm. To this end, the armature damper is configured in an annular shape (doughnut shape) so as to oppose to the one sides of the respective arms of the plurality of armatures which are disposed radially. A plurality of outer peripheral projections for positioning are provided at the outer periphery of the annular armature damper. The plurality of outer peripheral projections engage with projections which are provided at the inner periphery of an armature stopper disposed in an annual shape on the outer periphery side of the armature damper. According to this engagement relation, the armature damper is positioned and fixed so as to oppose to the one sides of the respective arms of the plurality of armatures.
Heretofore, the outer peripheral projections of the armature damper are assembled to have a small clearance with respect to the projections of the armature stopper. Usually, since the armature damper abuts against the arms of the armatures, the armature damper is formed by a rigid body with a high intensity. Thus, even when the outer peripheral projections of the armature damper are formed with a high accuracy, it is substantially difficult to assemble in such a manner that the clearance between the outer peripheral projections of the armature damper and the projections of the armature stopper is made zero thereby to completely make them coincide. As a result, as described above, there is a quite small clearance between the outer peripheral projections of the armature damper and the projections of the armature stopper.
At the time of the printing operation, since the arm of the armature repeatedly abuts against the armature damper at a high speed, the armature damper vibrates. Thus, there may arise such a phenomenon that the armature damper having been engaged with the armature stopper via the clearance deviates positionally due to the vibration, whereby the outer peripheral projections of the armature damper deviate from the projections of the armature stopper and so the armature damper is damaged.